EFFLUENT TREATMENT PROCESS - pH REFINEMENT FOR SULPHATE REMOVAL

Active Publication Date: 2019-01-03
MINTEK
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The invention aims to enhance the regeneration of aluminum hydroxide and reduce the formation of basic aluminum sulphate by decomposing ettringite at a pH of 8. The patent text explains that decomposing ettringite at a pH of 4 to 8.5 leads to poor regeneration of aluminum hydroxide and increased formation of basic aluminum sulphate. This pH range has been found to be the most suitable for enhancing the regeneration of aluminum hydroxide and reducing the formation of basic aluminum sulphate.

Problems solved by technology

The release of such waters into the environment poses a significant environmental challenge.

Method used

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  • EFFLUENT TREATMENT PROCESS - pH REFINEMENT FOR SULPHATE REMOVAL
  • EFFLUENT TREATMENT PROCESS - pH REFINEMENT FOR SULPHATE REMOVAL
  • EFFLUENT TREATMENT PROCESS - pH REFINEMENT FOR SULPHATE REMOVAL

Examples

Experimental program
Comparison scheme
Effect test

example 1

[0031]This example illustrates the effect of pH on the formation of aluminium precipitates.

[0032]The precipitation of various aluminium phases, namely aluminium trihydroxide (Al(OH)3), from sulphate media at pH values of 6.5, 7.0, 7.5, 8.0 and 8.5 was investigated. The effect of variations in pH on the types of solid phases formed was examined. The sulphate medium used consisted of aluminium sulphate solutions (Al2(SO4)3) prepared at 10 g / L. The pH of the medium was controlled with the addition of a caustic soda (NaOH) solution at a concentration of 500 g / L. Results from the precipitation tests revealed that the precipitated phases contained, in addition to aluminium, high amounts of sulphates. This indicated the formation of two phases, namely aluminium trihydroxide (Al(OH)3) and basic aluminium sulphate with the general formula (Al(OH)x(SO4)y). It was also found that the optimum pH for the formation of Al(OH)3 is in the range of 8.0 to 8.5. At this pH, the amount of basic aluminiu...

example 2

[0033]A fully integrated pilot plant operated as per the diagrams of the type shown in FIGS. 1 to 4 capable of processing 10 L / h of water, was operated for a period of 2 weeks. The combination of the heavy metal precipitation stage and the gypsum de-supersaturation stage was successful and average precipitation efficiencies of 98%, 97%, 96%, 96% and 25% were achieved for magnesium, manganese, aluminium, iron and sulphate respectively. The results in the ettringite precipitation stage showed that the target sulphate concentration of 400 mg / L (SANS Class I specification) in the overflow was reached, and potable water was produced after the carbonation stage in FIG. 3. The results from the ettringite decomposition stage showed a 99.5% recovery of amorphous aluminium trihydroxide precipitate.

example 3

[0034]This example illustrates heavy metal and gypsum precipitation, ettringite precipitation and ettringite decomposition steps of the invention.

[0035]A mini pilot plant capable of processing 100 L / h of acid mine water using the consolidated process of FIG. 1-4, was operated continuously for a period of four weeks. The feed to the plant consisted of a synthetic solution containing bivalent cations such as Mg2+, Ca2+, Mn2+, as well as SO42− and Fe2+. The average feed composition is presented in Table 2.

TABLE 2Feed water composition (expressed in mg / L)MgAlSiCaTiCrMn674262952239CoNiCuZnPbFeSO42−41308

[0036]The results of the pilot campaign showed that the process was effective at removing heavy metals from contaminated water. The treated water produced was nearly free of heavy metal ions, namely iron, aluminium, manganese and magnesium. Removal efficiencies of 97% and 93% were obtained for magnesium and manganese, respectively. Lime consumption was averaged at 1.4 kg / m3 of feed water.

[...

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Abstract

Disclosed is a method of decomposing ettringite, to form amorphous aluminium trihydroxide, which includes the step of lowering a pH of a slurry containing ettringite to a value between 8 and 8.5.

Description

BACKGROUND OF THE INVENTION[0001]This invention relates to a process for the removal of heavy metals, calcium and sulphate from contaminated water, typically mine waters.[0002]Effluent streams, and in particular acid mine drainage water, are generally acidic with pH values as low as 1,5. Another characteristic is the high levels of heavy metals, calcium and sulphate associated with the water. Prior to discharge into the environment these waste streams are normally neutralised with lime, a process which leaves large quantities of calcium sulphate in solution. The release of such waters into the environment poses a significant environmental challenge.[0003]International patent application number PCT / GB98 / 01610 describes a process, generally referred to as “the SAVMIN process”, which was developed particularly for the treatment of sulphate-containing mine waters as well as sulphate-containing waste / effluent waters. This process allows for the effective removal of sulphate and calcium f...

Claims

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Application Information

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IPC IPC(8): C02F1/52C02F1/66
CPCC02F1/5245C02F1/66C02F2001/5218C02F2303/18C02F2101/101C02F2101/20C02F2103/10C02F2209/06
Inventor KOTZE, MARTHA HENDRIETTE
Owner MINTEK
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